David Davis appears on the BBC’s Andrew Marr Show on Sunday.
Photograph: Getty Images

David Davis has clashed with the Irish government after claiming that the Brexit divorce agreement between Britain and the EU was a “statement of intent” rather than something legally enforceable.

The Brexit secretary’s comments came after it was reported that Downing Street advisers had told cabinet ministers who campaigned to leave the EU that promises around full regulatory alignment were “meaningless”.

Theresa May also appeared to suggest there was still some flexibility in the deal reached at the end of last week, writing to all Tory MPs – in a letter seen by the Guardian – to set out the details of the agreement but promising that “nothing is agreed until everything is agreed”.

In a statement issued after Davis had made his remarks to the BBC, the Irish government warned: “Both Ireland and the EU will be holding the UK to the phase one agreement.”

The deal, covering citizen rights, the divorce bill and promises around the Irish border, hit some last-minute difficulties but was signed off late last week – and is likely to result in EU leaders allowing talks to move on to the question of trade. The Irish deputy prime minister, Simon Coveney, highlighted a line in the agreement that said commitments relating to Ireland would be “upheld in all circumstances, irrespective of the nature of any future agreement between the EU and UK”.

Quick guide

Why is the Irish border a stumbling block for Brexit?

Counties and customs

Inside the EU, both Ireland and Northern Ireland are part of the single market and customs union so share the same regulations and standards, allowing a soft or invisible border between the two.

Britain’s exit from the EU – taking Northern Ireland with it – risks a return to a hard or policed border. The only way to avoid this post-Brexit is for regulations on both sides to remain more or less the same in key areas including food, animal welfare, medicines and product safety.

Early drafts of the agreement Britain hoped to get signed off on Monday said there would be “no divergence” from EU rules that “support north-south cooperation”, later changed to “continued alignment” in a formulation that appeared to allow for subtle divergences.

But it raised new questions about who would oversee it and how disputes might be resolved. It was also clearly still a step too far for the DUP.

Photograph: Design Pics Inc/Design Pics RF

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Joe McHugh, the Irish government’s chief whip, told the country’s RTE broadcaster: “We will as a government, a sovereign government in Ireland, be holding the United Kingdom to account, as will the European Union. My question to anybody within the British government would be: why would there be an agreement, a set of principled agreements, in order to get to phase two, if they weren’t going to be held up? That just sounds bizarre to me. This, as far as we’re concerned, is a binding agreement, an agreement in principle.”

EU leaders are expected to confirm this in a statement this week, warning that progress will not be made unless Friday’s agreement is “respected in full”.

Government sources insisted that Davis’s comments on BBC1’s Andrew Marr Show were simply echoing the European commission’s position that the legal agreement would be drawn up separately later in the process. They insisted “there is no question of our commitment to the text of the joint report”.

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But there was a further warning from Brussels about how the deal might work. A report on the progress of Brexit talks by the European commission said it would be difficult to reconcile the UK government’s two stated ambitions of no hard border between Ireland and Northern Ireland and leaving the single market and customs union.

The report also claimed that regulatory divergence between Northern Ireland and the republic was the “single biggest risk” to continued north-south cooperation. It said that Britain wanted to avoid a hard border through the overall EU-UK agreement, but added: “This intention seems hard to reconcile with the United Kingdom’s communicated decision to leave the internal market and the customs union.”

May will address parliament on Monday and declare a “new sense of optimism” around EU talks.

She will say “this is not about a hard or a soft Brexit” and insist that she has been entirely consistent in her arguments. However, one senior government official insisted that the prime minister and Davis expected the final deal to be a “soft” arrangement.

May’s comments in her statement to MPs will come before she embarks on internal cabinet discussions about what Brexit “end state” Britain should be seeking.

A meeting scheduled for next Tuesday is likely to pitch key ministers such as Philip Hammond, Amber Rudd and Greg Clark – who want the UK to remain closely aligned with the EU – with others including Boris Johnson and Michael Gove, who want the country to diverge.

May’s government will face a potential Tory rebellion this week over the EU withdrawal bill, as an amendment laid by Dominic Grieve calls for MPs to be given a vote before ministers can enact Brexit.

Labour’s Keir Starmer said his reading of the small print made that the idea that Britain could stay out of the single market and customs union while maintaining a soft border an impossible position. “Labour has been clear from the outset that Theresa May’s red lines on the negotiations were never going to be compatible with stopping a hard border in Northern Ireland,” he said.

“It is encouraging she has accepted that, but she cannot now be spooked by the extreme Brexiteers in her party. The agreement made last week should be treated as binding and was expressly intended to be part of the article 50 withdrawal agreement.

“Labour will not allow any rowing back on promises made that would put the union or the peace process at risk.”

Davis argued on Sunday that the chances of Britain crashing out of the EU without a trade deal had dropped dramatically and said that he expected a deal best described as a “Canada plus plus plus” arrangement.

That meant taking the best elements of deals already struck with countries such as Canada, Japan and South Korea, he told the BBC, and adding in services that were key to the British economy.

“The odds of a WTO [World Trade Organization] or no-deal scenario have dropped dramatically,” he said, admitting that he may not have been able to make that statement if last week’s negotiations had ended in deadlock, delaying trade talks until at least March.

Davis made clear that the promised divorce bill, which is expected to be between £35bn and £39bn, would be paid only once a trading arrangement had been agreed, saying “no deal means we won’t be paying the money.”

The comments represented a slapdown to Hammond. The chancellor claimed on Wednesday that it was “inconceivable that we are a nation would be walking away from an obligation that we recognised as an obligation”.

Davis said the substantive details of a trading arrangement must be in place by March 2019, although he conceded that “some minor negotiations” might continue as the UK entered a transitional period.

He said the deal could not be formally signed until Britain had left the EU, but that it could be done “one minute, or one second after we leave”.

Asked how Britain hoped to achieve its aims of a trade deal in eight months when it had taken Canada many years, Davis reiterated the government’s position that it was easier for the UK given that it already had the same standards as the EU.

He said it was highly significant that the divorce agreement referred to “full alignment”. “It was changed from no divergence and that’s the point. No divergence would have meant taking cut-and-paste rules,” he said.

Davis said, however, that full alignment would only affect a few sectors, such as agriculture, road and rail, and would mean the UK achieving certain outcomes but not necessarily in the same way as the EU did.

In her letter to MPs, May describes the idea of “full alignment” as “sharing the same policy goals even if we achieve them by different means”.